Programmed cell death-1 (PD-1) is an immune inhibitory receptor that is expressed transiently on the surface of CD4 and CD8 T cells following immune activation and is highly expressed on T cells chronically exposed to antigen. Signaling through PD-1 can result in T cell exhaustion, a state in which antigen-specific T cells no longer respond to antigen-specific stimulation. As observed in numerous persistent viral infections, including those from HIV, human hepatitis C virus, and murine lymphocytic choriomeningitis virus (LCMV), antibody blockade between PD-1 and its ligands (PD-L1/L2) results in the functional reactivation of exhausted antigen-specific T cells. Clinical trials incorporating a PD1 blockade therapy have demonstrated impressive success; highlighting the importance of the expression and regulation of this gene. Our work has shown that PD-1 is regulated at the level of transcription in a complex manner involving nine cis-regulatory elements; a network of positive (NFATc1 and STAT3) and negative (Blimp-1 and LSD1) transcription factors; and a dynamic epigenetic regulatory program, including DNA methylation. Despite this knowledge, the mechanistic details of how the cis-elements, trans-factors, and epigenetic pathways integrate to provide cell type and immune response regulation is not well understood. This understanding is important as PD-1's expression and activity is critical to the development of protective immune responses to infection and cancer. To elucidate the molecular mechanisms that govern PD-1 expression, we propose three aims designed to 1) define the cis- regulatory map and interactions at the PD-1 locus in antigen-specific cells following infection; 2) understand the interplay between NFATc1, Blimp-1 and STATs in regulating PD-1 during acute and viral infection conditions; and 3) to understand how the epigenetic silencer LSD1 controls PD-1 expression and DNA methylation at this locus. To investigate these aims, we have established a series of mouse lines that will conditionally delete the cis element CR-C, the transcription factor Blimp-1, or the epigenetic silencer LSD1 in activated CD8 T cells. We have established ex vivo methods to analyze the CD8 T cells and will incorporate an in vivo system of acute and chronic viral infection using LCMV to explore the mechanism by which these factors function to control PD-1. Ultimately our studies will elucidate the molecular genetic and epigenetic programs that control PD-1 expression and will provide new tools to manipulate PD-1 gene expression that could aid in the treatment of infection and cancer.